Volume 118, Issue 3, September 2005
Index of content:
- SPEECH PRODUCTION 
118(2005); http://dx.doi.org/10.1121/1.2001527View Description Hide Description
This study explores the effects of hearing status and bite blocks on vowel production. Normal-hearing controls and postlingually deaf adults read elicitation lists of ∕hVd∕ syllables with and without bite blocks and auditory feedback. Deaf participants’ auditory feedback was provided by a cochlear prosthesis and interrupted by switching off their implant microphones. Recording sessions were held before prosthesis was provided and one month and one year after. Long-term absence of auditory feedback was associated with heightened dispersion of vowel tokens, which was inflated further by inserting bite blocks. The restoration of some hearing with prosthesis reduced dispersion. Deaf speakers’ vowel spaces were reduced in size compared to controls. Insertion of bite blocks reduced them further because of the speakers’ incomplete compensation. A year of prosthesis use increased vowel contrast with feedback during elicitation. These findings support the inference that models of speech production must assign a role to auditory feedback in error-based correction of feedforward commands for subsequent articulatory gestures.
118(2005); http://dx.doi.org/10.1121/1.2000807View Description Hide Description
This study addressed an issue in the theory of acoustic invariance. The question was whether an invariant acoustic property exists for distinguishing Japanese single and geminate voiceless stops across rates and speakers. Four native Japanese speakers produced disyllabic words with single and geminate stops (e.g., /kako/ and /kak:o/) spoken in a carrier sentence at three speaking rates. Durations of sentences, words, stop closures, vowels preceding the contrasting stops, and voice onset times were measured. Ratios of geminate to single stop closures, geminate words to singleton words, closures to preceding vowels, and closures to words were calculated. The effect of rate on closure duration was to yield overlap between the singleton and geminate categories, and to lengthen geminate closures more than single closures as rate decreased. However, the ratio of geminate to single closure duration was unaffected by rate. Furthermore, the ratio of closure to word duration (0.35 as an optimal boundary) best classified all singleton and geminate tokens with 95.7%–98% accuracy. Thus, in spite of overlap in absolute closure duration between single and geminate voiceless stops, there is a relationally invariant measure that divides the two phonemic categories across rates and speakers, supporting the theory of relational acoustic invariance.
118(2005); http://dx.doi.org/10.1121/1.2000774View Description Hide Description
Previous research by speech scientists on the acoustic characteristics of American English vowel systems has typically focused on a single regional variety, despite decades of sociolinguistic research demonstrating the extent of regional phonological variation in the United States. In the present study, acoustic measures of duration and first and second formant frequencies were obtained from five repetitions of 11 different vowels produced by 48 talkers representing both genders and six regional varieties of American English. Results revealed consistent variation due to region of origin, particularly with respect to the production of low vowels and high back vowels. The Northern talkers produced shifted low vowels consistent with the Northern Cities Chain Shift, the Southern talkers produced fronted back vowels consistent with the Southern Vowel Shift, and the New England, Midland, and Western talkers produced the low back vowel merger. These findings indicate that the vowel systems of American English are better characterized in terms of the region of origin of the talkers than in terms of a single set of idealized acoustic-phonetic baselines of “General” American English and provide benchmark data for six regional varieties.
118(2005); http://dx.doi.org/10.1121/1.2000788View Description Hide Description
Previous research has established that naturally produced English clear speech is more intelligible than English conversational speech. The major goal of this paper was to establish the presence of the clear speech effect in production and perception of a language other than English, namely Croatian. A systematic investigation of the conversational-to-clear speech transformations across languages with different phonological properties (e.g., large versus small vowel inventory) can provide a window into the interaction of general auditory-perceptual and phonological, structural factors that contribute to the high intelligibility of clear speech. The results of this study showed that naturally produced clear speech is a distinct, listener-oriented, intelligibility-enhancing mode of speech production in both languages. Furthermore, the acoustic-phonetic features of the conversational-to-clear speech transformation revealed cross-language similarities in clear speech production strategies. In both languages, talkers exhibited a decrease in speaking rate and an increase in pitch range, as well as an expansion of the vowel space. Notably, the findings of this study showed equivalent vowel space expansion in English and Croatian clear speech, despite the difference in vowel inventory size across the two languages, suggesting that the extent of vowel contrast enhancement in hyperarticulated clear speech is independent of vowel inventory size.
118(2005); http://dx.doi.org/10.1121/1.2000787View Description Hide Description
The aerodynamic transfer of energy from glottal airflow to vocal fold tissue during phonation was explored using complementary synthetic and numerical vocal foldmodels. The synthetic model was fabricated using a flexible polyurethane rubber compound. The model size, shape, and material properties were generally similar to corresponding human vocal fold characteristics. Regular, self-sustained oscillations were achieved at a frequency of approximately 120 Hz. The onset pressure was approximately 1.2 kPa. A corresponding two-dimensional finite element model was developed using geometry definitions and material properties based on the synthetic model. The finite element model upstream and downstream pressureboundary conditions were based on experimental values acquired using the synthetic model. An analysis of the fully coupled fluid and solid numerical domains included flow separation and unsteady effects. The numerical results provided detailed flow data that was used to investigate aerodynamicenergy transfer mechanisms. The results support the hypothesis that a cyclic variation of the orifice profile from a convergent to a divergent shape leads to a temporal asymmetry in the average wall pressure, which is the key factor for the achievement of self-sustained vocal fold oscillations.